Image processing system, projector, method and computer program product

ABSTRACT

An image processing system includes a determination unit that determines a distortion state of a projected image, and a correction unit. The correction unit determines a shape of the image after distortion correction according to the distortion state, moves the determined shape in a display area of an optical modulator in a first direction, performs distortion correction of the image, and moves the image after distortion correction in the display area of the optical modulator in a second direction which is opposite to the first direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/186,662 filed Aug. 6, 2008, which claims priority from JapanesePatent Application No. 2007-205235 filed Aug. 7, 2007, each of which ishereby incorporated by reference in its entirety.

BACKGROUND

It is necessary for a projector to correct distortion of projectedimages for appropriate image display. For example, as disclosed inJapanese Patent Publication No. JP-A-2003-29714, a projector may performdistortion correction calculation using image information of inputimages. As an origin for the distortion correction calculation, for easycalculation, the midpoint of the lower side of a display area (liquidcrystal panel) or the point at the upper left of the display area isused as disclosed in Japanese Patent Publication No. JP-A-2003-29714.

However, when the midpoint of the lower side of the display area is usedas the origin, the distances to the upper left and the upper right ofthe image after distortion correction become longer, and, when the pointat the upper left of the display area is used, the distance to the lowerright of the image after distortion correction becomes longer. Thelonger the distance from the origin, the further an error of distortioncorrection calculation increases. On this account, when an image havinga laterally symmetric pattern, an image having a vertically symmetricpattern, an image with moire, or the like is projected using thesemethods, part of the patterns and moire are observed in a distortedcondition.

SUMMARY

An advantage of some aspects of the invention is to provide an imageprocessing system, a projector, a program, and an information storagemedium by which, even when an image having a laterally symmetric patternor the like is projected, an image without distorted pattern or the likecan be projected.

An image processing system according to an aspect of the inventionincludes a determination unit that determines a distortion state of aprojected image, and a correction unit that performs distortioncorrection of the image according to the distortion state, wherein thecorrection unit performs distortion correction calculation using eitheran intersection point of diagonal lines of the image after distortioncorrection in a display area of an optical modulator or a center ofgravity of the image as the origin.

Further, a projector according to an aspect of the invention includesthe above described image processing system and a projection unit thatprojects the image after distortion correction by the correction unit.

Furthermore, a program according to an aspect of the invention allows acomputer to perform the function of determining a distortion state of aprojected image, and correcting the distortion of the image according tothe distortion state, wherein the distortion correction calculation useseither an intersection point of diagonal lines of the image afterdistortion correction in a display area of an optical modulator or acenter of gravity of the image as the origin.

According to some aspects of the invention, since the image processingsystem or the like performs distortion correction calculation with theintersection point of diagonal lines of the image or the like as theorigin, it can perform the calculation nearly in the laterally andvertically symmetric condition with respect to the origin. Therefore,the calculation error can be reduced and the image without distortion ofpattern or the like can be generated. Further, according to some aspectsof the invention, since the intersection point of the diagonal lines ofthe image or the like corresponds to a position near the center of theprojected image, the projector or the like performs distortioncorrection calculation with the intersection point of diagonal lines ofthe image or the like as the origin, and thereby, it can project even animage having a laterally and horizontally symmetric pattern whilemaintaining the symmetry.

Additionally, the correction unit may perform the distortion correctioncalculation after moving the image after distortion correction withinthe display area so that the origin may coincide with a center of thedisplay area.

Thereby, the image processing system or the like can reduce the amountof calculation and perform more efficient calculation by performingdistortion correction calculation while making the origin coincide withthe center of the display area.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiment of the disclosure is described with reference to theaccompanying drawings, wherein like numbers reference like elements.

FIG. 1 shows an image after distortion correction in a liquid crystalpanel when an intersection point of diagonal lines is used as an origin.

FIG. 2 shows a state that the origin of the image after distortioncorrection in the liquid crystal panel is moved to the center of theliquid crystal panel.

FIG. 3 is a functional block diagram of a projector in the embodiment.

FIG. 4 is a flowchart showing a processing procedure of image distortioncorrection in the embodiment.

FIG. 5 shows a projected pattern image in a related art.

FIG. 6 shows a pattern image in the embodiment.

FIG. 7 shows a center of gravity of the image after distortioncorrection in the liquid crystal panel.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments in which the invention is applied to projectorswill be described with reference to the drawings. The followingembodiments do not impose any limitations on the description of theinvention described in claims. Further, all of the configurations shownin the following embodiments are not necessarily essential as solvingmeans for the invention described in claims.

First Embodiment

FIG. 1 shows an image after distortion correction in a liquid crystalpanel when the intersection point of diagonal lines is used as anorigin. Generally, the shape of an image before distortion correctionconforms to the shape of the liquid crystal panel which is a kind of adisplay area of an optical modulator. The coordinates on the fourcorners of the liquid crystal panel are denoted by A(x1,y1) , B(x2,y2),C(x3,y3), D(x4,y4) in the counterclockwise direction from the lowerleft, and the intersection point of the diagonal lines of the liquidcrystal panel is denoted by E. Further, the coordinates on the fourcorners of the image after distortion correction in the liquid crystalpanel are denoted by A′(x1′,y1′), B′(x2′,y2′), C′(x3′,y3′), D′(x4′,y4′)in the counterclockwise direction from the lower left, and theintersection point of the diagonal lines of the liquid crystal panel isdenoted by E′(x5′,y5′).

FIG. 2 shows a state that the origin of the image after distortioncorrection in the liquid crystal panel is moved to the center of theliquid crystal panel. Given that the above described point E is origino, and when the image after distortion correction is moved so that thepoint E′ may coincide with the origin o, the state shown in FIG. 2 isobtained. The number of effective pixels in the horizontal direction ofthe liquid crystal panel is denoted by W, and the number of effectivepixels in the vertical direction of the liquid crystal panel is denotedby H. In this case, A(x1,y1)=A(−W/2+1,−H/2+1), B(x2,y2)=B(W/2−1,−H/2+1),C(x3,y3)=C(W/2−1,H/2−1), D(x4,y4)=D(−W/2+1,H/2−1). Note that −1, +1 areadded because nonuse of the outermost pixels of the liquid crystal panelis specified, but −1, +1 are not necessarily added.

Further, the coordinates on the four corners of the image afterdistortion correction and moving in the liquid crystal panel are denotedby A″(x1″,y1″), B″(x2″,y2″), C″(x3″,y3″), D″(x4″,y4″) in thecounterclockwise direction from the lower left. In this case, the formerimage after distortion correction is moved by −x5′ in the horizontaldirection and by y5′ in the vertical direction, and thus,A″(x1″,y1″)=A″(x1′−x5′,y1′+y5′), B″(x2″,y2″)=B″(x2′−x5′,y2′+y5′),C″(x3″,y3″)=C″(x3′−x5′,y3′+y5′), D″(x4″,y4″)=D″(x4′−x5′,y4′+y5′) hold.

The coordinates on the four corners of the image after distortioncorrection A′(x1′,y1′), B′(x2′,y2′), C′(x3′,y3′), D′(x4′,y4′) areobtained by a projection angle or the like, the coordinates of theintersection point of the diagonal lines E′(x5′,y5′) are obtained fromthe coordinates on the four corners, and the numbers of effective pixelsH, W are known. Therefore, the projector can provide correspondencesbetween the coordinates and perform interpolation calculation or thelike even when the origin of the image after distortion correction ismoved to the center of the liquid crystal panel.

Next, functional blocks of the projector having the above describedfunctions will be described. FIG. 3 is a functional block diagram of aprojector 100 in the embodiment. The projector 100 includes an imageinformation input unit 120 that inputs image information (e.g., RGBsignals or the like), a distortion information input unit 110 thatinputs distortion information on distortion of a projected image, adetermination unit 130 that determines a distortion state of theprojected image based on the distortion information, a correction unit140 that corrects the distortion of the image according to thedistortion state, and a projection unit 190 that projects the imageafter distortion correction.

These respective units may be the following hardware. For example, thedistortion information input unit 110 may be a CCD sensor for imagingthe area containing the image projected on the screen, a button forinputting operation information when the image projected on the screencontaining distortion is operated to correct to the state withoutdistortion, an angle sensor that measures the projection angle, adistance sensor that measures the projection distance, etc. Further, theimage information input unit 120 may be an image signal input terminalor the like, the determination unit 130 may be a CPU or the like, thecorrection unit 140 may be an image processing circuit or the like, andthe projection unit 190 may be a lamp, liquid crystal panel, liquidcrystal drive circuit, projection lens, or the like.

Further, a computer of the projector 100 may mount the functions of thedetermination unit 130 etc. by reading programs from an informationstorage medium 200. As the information storage medium 200, for example,a CD-ROM, DVD-ROM, ROM, RAM, HDD, or the like may be applied, and thereading method of programs may be a contact method or non-contactmethod.

Next, a processing procedure of performing image distortion correctionusing the correction unit 140 etc will be described. FIG. 4 is aflowchart showing the processing procedure of image distortioncorrection in the embodiment. First, the distortion information inputunit 110 inputs distortion information by one of the above describedmethods (the method using the CCD sensor for imaging the projectedimage, the method of inputting correction operation information by auser, the method of measuring using the angle sensor and the distancesensor) (step S1). The projector 100 may project a calibration image(e.g., a wholly white image, image representing correction designation,or the like) prior to the processing at step S1.

The determination unit 130 determines a distortion state of theprojected image based on the distortion information from the distortioninformation input unit 110 (step S2). The correction unit 140 determinesthe shape of the image after distortion correction (e.g., A′, B′, C′, D′or the like shown in FIG. 1) according to the distortion state (stepS3). More specifically, in the case of the method of obtaining thecoordinates of A′, B′, C′, D′ based on the projection angle and theprojection distance, for example, the correction unit 140 firstcalculates three-dimensional coordinate values on the four corners inthe rectangular screen surface having the maximum rectangle that caninclude the image projected on the screen (also containing imagesoutside of the screen) and laterally symmetric with respect to thehorizontal short side at the same aspect ratio as the aspect ratio ofthe liquid crystal panel. Then, the correction unit 140 calculates thethree-dimensional coordinate values on the four corners in the abovedescribed rectangle in the condition that the liquid crystal panel isprojected on the surface inclined by the projection angle with theprojection optical axis being the normal line. Then, the correction unit140 can obtain the three-dimensional coordinate values of thecoordinates A′, B′, C′, D′ by calculating the three-dimensionalcoordinate values on the four corners in the rectangle after the liquidcrystal panel is returned to the condition with no inclination in thesurface, and can obtain two-dimensional coordinate values thereof.

Furthermore, as shown in FIG. 2, the correction unit 140 performsdistortion correction calculation with the intersection point as theorigin after moving the image after distortion correction so that theintersection point of the diagonal lines of the image after distortioncorrection may coincide with the center of the liquid crystal panel(step S4). Specifically, for example, the correction unit 140 performsimage interpolation using an interpolation method such as the bilinearmethod. In addition, the correction unit 140 may perform image colorcorrection, image brightness correction, or the like.

The correction unit 140 returns the image after image interpolation andthe like to the position shown in FIG. 1. The projection unit 190projects the image by a typical method of projecting the image afterdistortion correction (step S5).

FIG. 5 shows a projected pattern image 300 in a related art. Further,FIG. 6 shows a pattern image 301 in the embodiment. As seen from thecomparison between FIGS. 5 and 6, part of the projected pattern image300 may be distorted according to the technique in the related art.

On the other hand, according to the embodiment, since the projector 100performs distortion correction calculation with the intersection pointof diagonal lines of the image or the like as the origin, the projectorcan perform the calculation nearly in the laterally and verticallysymmetric condition with respect to the origin and the calculation inthe condition that the distances from the origin to apexes of the imageof interest are nearly equal when the shape of the image afterdistortion correction is nearly the rectangular shape. Therefore, thecalculation error can be reduced and the image without distortion ofpattern or the like as the pattern image 301 can be generated.

Further, according to the embodiment, since the intersection point ofthe diagonal lines of the image or the like corresponds to a positionnear the center of the projected image, the projector 100 performsdistortion correction calculation with the intersection point ofdiagonal lines of the image or the like as the origin, and thereby, theprojector can project even the pattern image 301 having the laterallysymmetric pattern while maintaining the symmetry, prevent the occurrenceof partial distortion as in the case of the pattern image 300 in therelated art, and improve the image quality.

Furthermore, according to the embodiment, the projector 100 can reducethe amount of calculation and perform more efficient calculation byperforming distortion correction calculation while making the origincoincide with the center of the liquid crystal panel.

Other Embodiments

The application of the disclosure is not limited to the above describedembodiment, but various changes can be made. For example, although theintersection point of diagonal lines of the image after distortioncorrection is used as the origin in the above described embodiment, theposition of the origin is not limited to the intersection point of thediagonal lines.

FIG. 7 shows the center of gravity G′ of the image after distortioncorrection in the liquid crystal panel. For example, as shown in FIG. 7,the center of gravity G′ (x6′,y6′) of the image after distortioncorrection may be used as the origin. As seen from the comparisonbetween FIGS. 1 and 7, even when the shape of the image after distortioncorrection is distorted in both vertical and horizontal directions, thecenter of gravity G′ is in a position at equal distances to therespective apexes D′ and B′, and A′ and C′, the calculation error isless likely to be caused, and thus, the projector 100 can projectappropriate images.

Further, although the correction unit 140 performs distortion correctioncalculation after moving the intersection point of the diagonal lines ofthe image after distortion correction to the center of the liquidcrystal panel, the unit may perform the distortion correctioncalculation without moving the intersection point of the diagonal linesof the image after distortion correction.

Furthermore, the projector 100 is not limited to the liquid crystalprojector, but may be a projector using DMD (Digital MicromirrorDevice). The DMD is a registered trademark of Texas Instruments, Inc.,U.S. Additionally, the function of the projector 100 may be distributedand mounted in plural devices (e.g., PC and projector, or the like).

What is claimed is:
 1. An image processing system comprising: adetermination unit that determines a distortion state of a projectedimage; and a correction unit that determines a shape of the image afterdistortion correction according to the distortion state, moves thedetermined shape in a display area of an optical modulator in a firstdirection, performs distortion correction of the image, and moves theimage after distortion correction in the display area of the opticalmodulator in a second direction which is opposite to the firstdirection.
 2. A projector comprising: the image processing systemaccording to claim 1; and a projection unit that projects the imageafter distortion correction by the correction unit.
 3. An imageprocessing method, comprising: determining a distortion state of aprojected image; determining a shape of image after distortioncorrection according to the distortion state; moving the determinedshape in a display area of an optical modulator in a first direction;performing distortion correction of the image, and moving the imageafter distortion correction in the display area of the optical modulatorin a second direction which is opposite to the first direction.
 4. Acomputer program product embodied in at least one computer readablemedium and comprising computer instructions executable by a computingdevice to perform the function of: determining a distortion state of aprojected image; determining a shape of image after distortioncorrection according to the distortion state; moving the determinedshape in a display area of an optical modulator in a first direction;performing distortion correction of the image, and moving the imageafter distortion correction in the display area of the optical modulatorin a second direction which is opposite to the first direction.